Placement of an articular prosthesis at the ankle of a patient during a surgical operation, typically from an anterior approach path, requires preparation notably by resections, of the lower end of the tibia, as well as often the upper end of the talus of the patient, in order to permanently fix thereon the tibia and talus implants belonging to the ankle prosthesis. In practice, once the bone preparations are carried out, the surgeon frequently resorts to phantoms of prosthetic implants, allowing the surgeon to make sure that these preparations are suitable and that additional bone cutting or additional resurfacings are not necessary. These phantoms are not necessarily of the same shape as the corresponding implant.
Sometimes, a patient may be fitted with an initial fitted ankle prosthesis, and the initial implantation may be revised subsequently; in the case of a revision, the talar implant is often provided with a talo-calcaneal anchoring keel, which may be sufficiently long for stabilizing the talus implant facing both the talus and the calcaneus of the patient. This being said, this type of ankle prosthesis with a long keel may of course be positioned as a first intention prosthesis, notably if the bones of the foot are highly damaged. It is understood that the positioning instrumentation for an ankle prosthesis with a long keel should allow the surgeon to prepare the talus and the calcaneus accordingly, so that these bones are ready to receive the aforementioned long keel in an ad hoc housing. Further, in spite of all the care which the surgeon may provide in handling such instrumentation, notably with a significant intervention time, the risks are not negligible that the preparation of the aforementioned housing might be not satisfactory, in the sense that the implantation of the talus component resulting from this does not allow good subsequent articular cooperation with the tibial component attached to the tibia.